Recently, Mobile IP has increasingly been studied in mobile communications (for example, Non-patent Document 1).
Mobile IP is a protocol for automatically detecting a migration of a terminal between networks and enabling communications in a network after the migration in the same way as in a network before the migration. Mobile IP compensates for migrations in IP level, and has characteristics that the IP is not dependent on an application to use and techniques under layer 2.
The schematic operation of Mobile IP will be described below. FIGS. 1A and 1B are schematic diagrams illustrating Mobile IP, where FIG. 1A is a schematic diagram illustrating Mobile Ipv4, and FIG. 1B is a schematic diagram illustrating Mobile Ipv6.
As shown in FIG. 1A, procedures for registering a care-of address in Mobile Ipv4 are as follows: 1. A terminal moves to a cell (step ST11). 2. The terminal receives an Agent Advertisement periodically transmitted from a FA (Foreign Agent) (step ST12). 3. The terminal acquires a care-of address from the Agent Advertisement. 4. The terminal registers the care-of address with the FA (step ST13). 5. The FA registers the care-of address with a Home Agent (step ST14).
The FA is not necessary in Mobile Ipv6. Therefore, the use of Mobile Ipv6 has been discussed widely. Each terminal has a unique address called the home address, and uses a care-of address in a migration place. Accordingly, each terminal is assigned a care-of address as well as the home address. Each terminal needs to register the care-of address with the Home Agent when migrating to another cell. As shown in FIG. 1B, the registration of a care-of address is carried out in following procedures: 1. A terminal moves to another cell (step ST21). 2. The terminal receives a Router Advertisement periodically transmitted from an Access Router (step ST22). 3. The terminal generates a care-of address from the Router Advertisement. 4. The terminal registers the care-of address with the Home Agent (step ST23).
There is a method of installing a Mobility Anchor Point (hereinafter abbreviated as “MAP”) on an upper layer of a plurality of Access Routers (hereinafter abbreviated as “ARs”) to cause hierarchical registration of care-of address, and thereby intending fast handover and reduction in load on the Home Agent (herein after abbreviated as “HA”). FIG. 2 is a diagram illustrating a configuration of a mobile IP network using MAPs.
A Mobile Node (hereinafter abbreviated as “MN”) needs to register a care-of address with the MAP as well as the HA. The MN detects Prefixes of the MAP and AR from the Router Advertisement (hereinafter abbreviated as “RA”) transmitted from the AR, and using the Prefixes and an Interface Identifier of the MN, generates two care-of addresses, a Regional Care-Of Address (hereinafter abbreviated as “RCOA”) and On-Link Care-Of Address (hereinafter abbreviated as “LCOA”). Only the RCOA needs to be registered with the HA, and the number of registrations with the HA is significantly reduced. When moving between ARs, a change in LCOA is required, but only registration with the MAP is necessary. Since the MAP exists relatively nearer than the HA, registration time is short, enabling fast handover. In FIG. 2, AR1 to AR8 use the same LCOA, while AR9 to AR16 use the same LCOA.
The aforementioned operation is shown in FIG. 3. FIG. 3 is a flow diagram illustrating an example of the operation in the conventional network.
Initial setting is performed in ST51. In ST52, it is determined whether a terminal has moved between MAPs. When the terminal has moved between MAPs, the processing flow proceeds to ST53. When the terminal has not moved between MAPs, the processing flow proceeds to ST54. In ST53, the RCOA is registered with the HA. In ST54, the LCOA is registered with the MAP, and the processing flow returns to ST52. A list of terms of Mobile IP is shown in Table 1.
[Table 1]
However, in the aforementioned constitution using MAPs, it is necessary to register the care-of address with both the MAP and HA in handover between MAPs. It is thus an issue to reduce delay time in handover between MAPs.
In order to overcome the aforementioned issue, i.e. to reduce the delay time in handover between MAPs, a method is considered for installing MAPs hierarchically (for example, Non-patent Document 2).
Non-patent Document 1: Charles E. Perkins, “Mobile IP”, IEICE Communications Magazines, MAY 2002,
Non-patent Document 2: Kono, et al., “Study on Terminal Mobility Analogy Method for Multilayer Dispersive IP Mobility Control System, CQ2002-77.